Extendable mechanism

ABSTRACT

An extendable mechanism is provided which may be freely designed in order to produce a force required for a given purpose of use. The mechanism generally comprises a pantograph or cross linkage, a pair of auxiliary links each of which is hinged to each of a pair of main links of the pantograph or cross linkage at a point between the pin joints of each link, and an extending device such as a hydraulic jack which is interposed of the pin joint between said pair of links and the joint of the pair of auxiliary links.

United States Patent 1 1 111 3,806,093 Itazu 5] Apr. 23, 1974 [54] EXTENDABLE MECHANISM 1,902,827 3/1933 Bolens 254/93 H [75] Inventor: Fumio Itazu, Minokamo, Japan 1 O IGN PATENTS OR APPLICATIONS Assignees: Kayabakogyo abushi i i Canada y Kabushikikaisha 623,956 3/1927 France Towaseis k sho, M k 1,025,811 3/1958 Germany 254/12 1 both Japan Primary Examiner-Othell M. Simpson [22] Filed: Nov. 8, 1972 Assistant Examiner--Robert C. Watson pp No: 304,804 Attorney, Agent, or Firm-Saul Jecres [57] ABSTRACT Foreign Application Priority Data An extendable mechanism is provided which may be Nov. 8, 1971 Japan 46-88248 freely designed in order to produce a force required for a given purpose of use. The mechanism generally [52] US. Cl. 254/124, 254/93 H comprises a pantograph or cross linkage, a pair of aux- [51 Int. Cl B66f 3/00 iliary links each of which is hinged to each of a pair of [58] Field of Search ..254/l2 4, 126,122, 931-1 main links of the pantograph or cross linkage ata 182/157, 158 point between the pin joints of each link, and an extending device such as a hydraulic jack which is inter- [56] References Cited posed of the pin joint between said pair of links'and UNITED STATES PATENTS the joint of the pair of auxiliary links.

3,259,369 7/1966 Gridley 254/122 6 Claims, 7 Drawing Figures ymgmgnmzs 1914 I 3806.093

' sum 1 0F 4 PATENTEDAPR23 19M 3,806,095

SHEET 3 OF 4 28 W2 28 y lo F|G.3 p, M

L5 L2 L5 (U26 '4 d, L5 I '4 26b -64 w 32 68 68 32 (av re) x 1 .EXTENDABLE MECHANISM BACKGROUND OF THE INVENTION The present invention relates generally to an extendable mechanism using a pantograph or cross linkage, and more particularly to an extendable mechanism best adapted for use as a lift.

Pantograph jacks and table lifters are typical lift devices using a pantograph or cross linkage. A pantograph jack generally comprises a pantograph linkage and a screw threaded to the opposed joints of the link-- age. The spacing between the opposed joints may be increased or decreased by turning the screw. A table lifter generally comprises a base and a table coupled to each other by a parallel or cross linkage. The table is lifted by a hydraulic hoist interposed between the base and the linkage. In both the pantograph jack and table lifter the maximum force required when the jack or lifter starts to lift because of their mechanisms. The lifting force is gradually decreased as the'jack or table lifter is lifted. The lift speed is also fastest when the jack or table starts to lift and is gradually decreased as the jack or table is lifted. Thus the lifting force and the lift speed cannot be freely selected depending upon the purpose of use, so that the design for the conventional pantograph jacks and table lifters are extremely difficult.

SUMMARY OF THE INVENTION One of the objects of the present invention is therefore to provide an improved extendable mechanism, using a pantograph or cross linkage which may be freely designed in order to provide any desired extending or lift force and speed or lift speed. Briefly described, according to the present invention a pair of auxiliary links are hinged to a pair of main links of a pantograph or cross linkage at a suitable point between the two pin joints of each link, and an extending device such as a hydraulic jack is interposed between the pin joint of the pair of auxiliary links and the pin joint between said pair of main links. The extending or lifting Lli force as well as the extending or lift speed may be freely selected over the full lift stroke by selecting the point at which the pair of auxiliary main links are hinged to the pair of links.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of some preferred embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. illustrates a pantograph jack l0 embodying the present invention, but it will be understood that the present invention may be also applied to various link- 2 ages. The pantograph jack 10 generally comprises a hydraulic jack 12, which also serves as a base, a pair of lower links 14, a pair of upper links 16 and a saddle 18 for receiving a load.

A pair of flanges 22 are formed at both sides of a seat 20 of the hydraulic jack 12 in opposed relation. Each of the lower links 14 comprises a pair of steel plates or the like whose lower ends are rotatably pivoted to the flanges 22 with pins 24. Each of the upper links 16 comprises a channel-shaped steel member whose lower end is hinged to the upper end of the lower link 14 with a pin 26. An elongated slot 34 is formed in the base of each channel-shaped upper link 16 in order to reduce the weight. The upper ends of the pair of upper links 16 are rotatably coupled to each other through the saddle l8 and saddle plates 38 with pins 28. It should be noted that teeth 36 are formed at the upper ends of the upper links 16 and engaged with each other when assernbled.

In the instant embodiment the hydraulic jack 12 may be a conventional portable jack so that it will be briefly described in this specification. That is, the hydraulic jack 12 generally comprises a main body 40 which in turn comprises a tank and a cylinder tube, a ram 42 slidably fitted into the cylinder tube, a pump 44 for pumping the working oil from the tank in the main body 40 into the cylinder tube for thereby lifting the ram 42, and a pressure-relief valve 46 for returning the working oil from the cylinder tube to the tank for thereby lowering the ram 42. All of the above described component parts of the hydraulic jack 12 are mounted on the seat 20. The pump 44 generally comprises a pump cylinder 48 fixed to the seat 20, a plunger 50 slidably fitted into the cylinder 48, and a coupling member 54 for receiving an operating lever 52. The coupling member 54 is pivoted with a pin 62 to the plunger 50 and also connected at one end thereof to the seat 20 through a connecting plate 56 with pins 58 and 60.

A connecting member 64 securely fixed to the upper endofthe ram 42 of the hydraulic jack 12 has a pair of extensions 66 whose width is smaller than the spacing between the pair of steel members forming each lower link-14. A pair of auxiliary links 68, which are the most important components of the present invention, are 'in the form of a yoke and have their one ends hinged with pins 30 to the extensions 66 of the connecting member 64 respectively, and their. other ends hinged with pins 32 to the lower links 14.

Next the mode of operation will be described First the operating lever 52 is fitted into the coupling member 54 of the pump 44 and swung to reciprocate the plunger 50 in the pump cylinder 48. Therefore the working oil in the tank of the main body 40 is drawn and forced into the bottom of the cylinder tube, thereby forcing the ram 42 to move up. The connecting member 64 fixed to the ram 42 is raised so that the lower links 14 are also lifted by the auxiliary links 68. As a result both the upper and lower links 16 and 14 are extended. When the operating lever 52 is fitted onto and turns the pressure relief valve 46, the latter is opened so that the working oil in the cylinder tube is returned to the tank. As a result the lower and upper links 14 and 16 are contracted or lowered under the force of the load exerted upon the saddle 18. In the extension and contraction of the pantograph jack the movement of the lower links 14 is controlled by the connecting member 64 through the auxiliary links 68, whereas the movement of the pair of upper links 16 is controlled by the teeth 36 which engage with each other at the upper ends of the upper links 16. Therefore the pantograph consisting of the hydraulic jack 12, the lower and upper links 14 and 16 and the saddle 18 may always maintain its correct form so that the saddle 18 may be always maintained in the horizontal position.

. Instead of the hydraulic jack a working oil source such as a hand or power pump may be disposed independently of the pantograph jack and hydraulically coupled through a tube or the like to a hydraulic cylinder interposed between the seat 20 and the connecting member 64, so that the pantograph jack may be remote-controlled. In some cases, the lower and upper links 14 and 16 cannot be completely contracted by their own weight. In order to overcome this problem,-

return springs 74 may be connected, as shown in FIG. 2, between abase 70 upon which is mounted the hydraulic jack 12 and a pair of arms 72 extended from the connecting member 64.

From the foregoing description the construction and mode of operation of the pantograph jack l embodying the present invention are apparent to those skilled in the art. Next the relation between the lift x of the hydraulic jack 12 and the lift y of the pantograph jack and the relation between the load W2 applied to the saddle 18 and the force exerted to the connecting member 64 will be described in detail.

Referring to FIG. 3 illustrating diagrammatically the principle of the pantograph jack 10, for the sake of convenience of explanation the pins 24 coupling the lower links 14 to the seat of the hydraulic jack 12 will be referred to as a; the pins 26 coupling the lower and upper links 14 and 16 together, b; the pins 28 coupling the upper links 16 to the saddle 18, c; the pins 30 coupling the auxiliary links 68 to the connecting member 64, d; and the pins 32 coupling the lower links 14 to the auxiliary links 68, e. It is assumed that the distance between a and a be the distance between 0 and c, 1 the distance between d and d, 1 the distance between a and b, 1;; the distance between b and c, 1 the distance between a and e, 1 and the distance between d and e, 1 Furthermore it is assumed that l =l =13, and

Next referring to FIG. 4, from the relation 1 1 x 2-l 'xcos6 cos 0 of the triangle a, d, e is given by 'Since ab bc =1 the triangle 0, b, c is an isosceles triangle. Hence, 0 6.. Therefore the lift of the pantograph jack 10 is given by 4/ 6( 6 X2 1 4 e' l 7 6 The ratio of the stroke of the hydraulic jack 12 to the lift of the pantograph jack 10 is given by 4/16' 1 6 The ratio of the load exerted on the pantograph jack 10 to the load exerted on the hydraulic jack 12 is given by the law of conservation of energy (W alx W dy) by 4/ s'l 1 e )l If the distance equals the distance 1 y 4 6 and 1 2 4/ 6 It is seen that the stroke ratio y/x and the load ratio W1/ W are always equal, independently of the stroke x of the hydraulic jack 12. This means that when the hydraulic jack -12 is extended or contracted at a constant speed, the pantograph jack 10 is lifted or lowered at a constant speed equal to /1 of the speed of the hydraulic jack 12 and that when the load exerted to the pantograph jack 10 remains unchanged, the load W exerted to the hydraulic jack also remains unchanged over the full stroke thereof.

However, when 1 1 y 4 sl 6 1 71 4/16 1/ 2 q/ el 1 (6 7 )l 4/ 6 It is seen that the stroke ratio y/x is decreased as the stroke x of the hydraulic jack 12 increases and so is the load ratio W /W This means that the force of the hydraulic jack 12 is minimum when the pantograph jack 10 starts to 'lift from the most contracted position and is gradually increased as the lift of-the pantograph jack 10 is increased. Furthermore, the lift speed of the pantograph jack 10 with respect to that of the hydraulic jack 12 increases as the lift of the pantograph jack 10 is increased.

When 1 l, y/x 4/ e'l 7 6 4/ 6 1/ 2 4/ 6 7 6 )l 4/ 6 Therefore, as the stroke x-of' the hydraulic jack 12 increases, the stroke ratio y/x increases whereas the load ratio W,/W decreases. This means that as the pantograph jack 10 is raised the lift speed of the pantograph jack 10 with respect to that of the hydraulic jack 12 decreases, but the lift force becomes maximum when the pantograph jack 10 is about to be fully extended or lifted. From the foregoing description a pantograph jack best adapted for the purpose of use may be freely designed by selecting a suitable'length for the auxiliary link 68 and. a position at which the auxiliary link 68 is connected to the lower link 14. So far it has been assumed that 1 l l and I 15, but it will be understood that the above relations may be changed depending upon the purpose of the pantograph jack. Therefore the principle of the present invention may be also applied to a linkage 10a of the type shown in FIG. 5, a parallel linkage 10b of the type shown in FIG. 6 and a cross linkage 10a of the type shown in FIG. 7. The linkage l0a shown'in FIG. 5 consists of two pantograph linkages, and the linkage 10b shown in FIG. 6 is also a pantograph because the lower and right links may be considered as lower links 14 shown in FIG. 1, whereas the upper and left links may be considered as upper links 16. The cross linkage 10c shown in FIG. 7 may be also considered as a pantograph because two links indicated by the chain lines-of a pantograph may be considered to be extended toward the base 20.

The present invention has been described in detail with particular reference to the preferred embodiments thereof but it will be understood that variations and modifications can be effected within the .spirit and scope of the present invention as described hereinabove and as defined in the appended claims.

What is claimed is:

1. An extendible mechanism; comprising a pantograph linkage including a pair of first links having first and second ends, a pair of second links also having first and second ends, first pivot means pivotably connecting said first ends of said first links, second pivot means pivotably connecting said second ends of said second links, and third pivot means pivotably connecting said second ends of said first links with said first ends of said second links;

a pair of auxiliary links having first ends which are pivoted to one another, and also having second ends;

fourth pivot means pivotably connecting each of said second ends of said auxiliary links with one of said second links intermediate said first and second pivot means in the region of the latter; and

an extendible device connected with said first ends of said auxiliary links and operative for displacing the latter in direction towards said first pivot means.

2. An extendible mechanism as defined in claim 1,

wherein said extendible device comprises a hydraulic jack.

3. An extendible mechanism as defined in claim 2,

wherein said hydraulic jack comprises a base, and wherein said second pivot means comprises two second pivots each of which pivotably connects one of said second ends of said second links with said base of said hydraulic jack; further comprising a load-engaging saddle; and wherein said first pivot means comprises two vfirst pivots each of which pivotably connects one of said first ends of said first links with said saddle.

4. An extendible mechanism as defined in claim 3. wherein said hydraulic jack further comprises a ram having a free end portion, and a connecting member fixed to said free end portion; and further comprising a pair of auxiliary pivotseach pivotably connecting one of said first ends of said auxiliary links with said connecting member.

5. An extendible mechanism as defined in claim 3, wherein said first ends of said first links are formed with teeth which inter-engage with one another.

6. An extendible mechanism as defined in claim 3; and further comprising return spring means connected between said connecting member and said base and permanently urging the former to move towards the latte'r. v 

1. An extendible mechanism, comprising a pantograph linkage including a pair of first links having first and second ends, a pair of second links also having first and second ends, first pivot means pivotably connecting said first ends of said first links, second pivot means pivotably connecting said second ends of said second links, and third pivot means pivotably connecting said second eNds of said first links with said first ends of said second links; a pair of auxiliary links having first ends which are pivoted to one another, and also having second ends; fourth pivot means pivotably connecting each of said second ends of said auxiliary links with one of said second links intermediate said first and second pivot means in the region of the latter; and an extendible device connected with said first ends of said auxiliary links and operative for displacing the latter in direction towards said first pivot means.
 2. An extendible mechanism as defined in claim 1, wherein said extendible device comprises a hydraulic jack.
 3. An extendible mechanism as defined in claim 2, wherein said hydraulic jack comprises a base, and wherein said second pivot means comprises two second pivots each of which pivotably connects one of said second ends of said second links with said base of said hydraulic jack; further comprising a load-engaging saddle; and wherein said first pivot means comprises two first pivots each of which pivotably connects one of said first ends of said first links with said saddle.
 4. An extendible mechanism as defined in claim 3, wherein said hydraulic jack further comprises a ram having a free end portion, and a connecting member fixed to said free end portion; and further comprising a pair of auxiliary pivots each pivotably connecting one of said first ends of said auxiliary links with said connecting member.
 5. An extendible mechanism as defined in claim 3, wherein said first ends of said first links are formed with teeth which inter-engage with one another.
 6. An extendible mechanism as defined in claim 3; and further comprising return spring means connected between said connecting member and said base and permanently urging the former to move towards the latter. 